OBSERVATION OF THE ROOM-TEMPERATURE TE-125 MOSSBAUER-EFFECT IN MG3TEO6 - LINEWIDTH, RECOIL-FREE FRACTION, AND ISOMER-SHIFT

Fifty-eight-day Te-125m in a Mg3TeO6 host provides an easily produced, rugged, high recoil-free fraction and narrow-emission-linewidth sourc e for Te-125 Mossbauer spectroscopy. The high f factor of this source opens the possibility of precision T-dependent Mossbauer-spectroscopy measurements in Te-bearing compounds with the source kept at room temp erature. Using such a source at 300 K, we have measured the T dependen ce of the f factor for both Mg3TeO6 and cubic ZnTe absorbers and find Debye temperatures THETA(D) of 390(2) K and 188(2) K, respectively. At 300 K, the f factor of MG3TeO6 (0.46) is found to be an order of magn itude larger than in cubic ZnTe (0.040) thus making feasible room-temp erature observation of the Mossbauer effect with the oxide source. Bot h emission and absorption linewidths of the oxide matrix have been exa mined and display a 14(3)% line broadening over the natural width (GAM MA(n)), a result that is thought to be intrinsic to the oxide host. Th e isomer shift of Te metal (78 K) and cubic ZnTe (78 K) relative to Mg 3TeO6 at 300 K is +1.86(9) and +1.21(3) mm/s, respectively. Mg3TeO6 is easily prepared in a pure form and yields reproducible crystal struct ure and Mossbauer-effect parameters. Mg3TeO6 provides a suitable stand ard matrix for Te-125 isomer shift and f-factor measurements.